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 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
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/*
 * (C) Copyright Taligent, Inc. 1996 - All Rights Reserved
 * (C) Copyright IBM Corp. 1996 - All Rights Reserved
 *
 *   The original version of this source code and documentation is copyrighted
 * and owned by Taligent, Inc., a wholly-owned subsidiary of IBM. These
 * materials are provided under terms of a License Agreement between Taligent
 * and Sun. This technology is protected by multiple US and International
 * patents. This notice and attribution to Taligent may not be removed.
 *   Taligent is a registered trademark of Taligent, Inc.
 *
 */

package java.util;

import java.io.Serializable;
import java.security.AccessController;
import java.security.PrivilegedAction;
import java.time.ZoneId;
import sun.security.action.GetPropertyAction;
import sun.util.calendar.ZoneInfo;
import sun.util.calendar.ZoneInfoFile;
import sun.util.locale.provider.TimeZoneNameUtility;

/**
 * <code>TimeZone</code> represents a time zone offset, and also figures out daylight
 * savings.
 *
 * <p>
 * Typically, you get a <code>TimeZone</code> using <code>getDefault</code>
 * which creates a <code>TimeZone</code> based on the time zone where the program
 * is running. For example, for a program running in Japan, <code>getDefault</code>
 * creates a <code>TimeZone</code> object based on Japanese Standard Time.
 *
 * <p>
 * You can also get a <code>TimeZone</code> using <code>getTimeZone</code>
 * along with a time zone ID. For instance, the time zone ID for the
 * U.S. Pacific Time zone is "America/Los_Angeles". So, you can get a
 * U.S. Pacific Time <code>TimeZone</code> object with:
 * <blockquote><pre>
 * TimeZone tz = TimeZone.getTimeZone("America/Los_Angeles");
 * </pre></blockquote>
 * You can use the <code>getAvailableIDs</code> method to iterate through
 * all the supported time zone IDs. You can then choose a
 * supported ID to get a <code>TimeZone</code>.
 * If the time zone you want is not represented by one of the
 * supported IDs, then a custom time zone ID can be specified to
 * produce a TimeZone. The syntax of a custom time zone ID is:
 *
 * <blockquote><pre>
 * <a name="CustomID"><i>CustomID:</i></a>
 *         <code>GMT</code> <i>Sign</i> <i>Hours</i> <code>:</code> <i>Minutes</i>
 *         <code>GMT</code> <i>Sign</i> <i>Hours</i> <i>Minutes</i>
 *         <code>GMT</code> <i>Sign</i> <i>Hours</i>
 * <i>Sign:</i> one of
 *         <code>+ -</code>
 * <i>Hours:</i>
 *         <i>Digit</i>
 *         <i>Digit</i> <i>Digit</i>
 * <i>Minutes:</i>
 *         <i>Digit</i> <i>Digit</i>
 * <i>Digit:</i> one of
 *         <code>0 1 2 3 4 5 6 7 8 9</code>
 * </pre></blockquote>
 *
 * <i>Hours</i> must be between 0 to 23 and <i>Minutes</i> must be
 * between 00 to 59.  For example, "GMT+10" and "GMT+0010" mean ten
 * hours and ten minutes ahead of GMT, respectively.
 * <p>
 * The format is locale independent and digits must be taken from the
 * Basic Latin block of the Unicode standard. No daylight saving time
 * transition schedule can be specified with a custom time zone ID. If
 * the specified string doesn't match the syntax, <code>"GMT"</code>
 * is used.
 * <p>
 * When creating a <code>TimeZone</code>, the specified custom time
 * zone ID is normalized in the following syntax:
 * <blockquote><pre>
 * <a name="NormalizedCustomID"><i>NormalizedCustomID:</i></a>
 *         <code>GMT</code> <i>Sign</i> <i>TwoDigitHours</i> <code>:</code> <i>Minutes</i>
 * <i>Sign:</i> one of
 *         <code>+ -</code>
 * <i>TwoDigitHours:</i>
 *         <i>Digit</i> <i>Digit</i>
 * <i>Minutes:</i>
 *         <i>Digit</i> <i>Digit</i>
 * <i>Digit:</i> one of
 *         <code>0 1 2 3 4 5 6 7 8 9</code>
 * </pre></blockquote>
 * For example, TimeZone.getTimeZone("GMT-8").getID() returns "GMT-08:00".
 *
 * <h3>Three-letter time zone IDs</h3>
 *
 * For compatibility with JDK 1.1.x, some other three-letter time zone IDs
 * (such as "PST", "CTT", "AST") are also supported. However, <strong>their
 * use is deprecated</strong> because the same abbreviation is often used
 * for multiple time zones (for example, "CST" could be U.S. "Central Standard
 * Time" and "China Standard Time"), and the Java platform can then only
 * recognize one of them.
 *
 * @author Mark Davis, David Goldsmith, Chen-Lieh Huang, Alan Liu
 * @see Calendar
 * @see GregorianCalendar
 * @see SimpleTimeZone
 * @since JDK1.1
 */
abstract public class TimeZone implements Serializable, Cloneable {

  /**
   * Sole constructor.  (For invocation by subclass constructors, typically
   * implicit.)
   */
  public TimeZone() {
  }

  /**
   * A style specifier for <code>getDisplayName()</code> indicating
   * a short name, such as "PST."
   *
   * @see #LONG
   * @since 1.2
   */
  public static final int SHORT = 0;

  /**
   * A style specifier for <code>getDisplayName()</code> indicating
   * a long name, such as "Pacific Standard Time."
   *
   * @see #SHORT
   * @since 1.2
   */
  public static final int LONG = 1;

  // Constants used internally; unit is milliseconds
  private static final int ONE_MINUTE = 60 * 1000;
  private static final int ONE_HOUR = 60 * ONE_MINUTE;
  private static final int ONE_DAY = 24 * ONE_HOUR;

  // Proclaim serialization compatibility with JDK 1.1
  static final long serialVersionUID = 3581463369166924961L;

  /**
   * Gets the time zone offset, for current date, modified in case of
   * daylight savings. This is the offset to add to UTC to get local time.
   * <p>
   * This method returns a historically correct offset if an
   * underlying <code>TimeZone</code> implementation subclass
   * supports historical Daylight Saving Time schedule and GMT
   * offset changes.
   *
   * @param era the era of the given date.
   * @param year the year in the given date.
   * @param month the month in the given date. Month is 0-based. e.g., 0 for January.
   * @param day the day-in-month of the given date.
   * @param dayOfWeek the day-of-week of the given date.
   * @param milliseconds the milliseconds in day in <em>standard</em> local time.
   * @return the offset in milliseconds to add to GMT to get local time.
   * @see Calendar#ZONE_OFFSET
   * @see Calendar#DST_OFFSET
   */
  public abstract int getOffset(int era, int year, int month, int day,
      int dayOfWeek, int milliseconds);

  /**
   * Returns the offset of this time zone from UTC at the specified
   * date. If Daylight Saving Time is in effect at the specified
   * date, the offset value is adjusted with the amount of daylight
   * saving.
   * <p>
   * This method returns a historically correct offset value if an
   * underlying TimeZone implementation subclass supports historical
   * Daylight Saving Time schedule and GMT offset changes.
   *
   * @param date the date represented in milliseconds since January 1, 1970 00:00:00 GMT
   * @return the amount of time in milliseconds to add to UTC to get local time.
   * @see Calendar#ZONE_OFFSET
   * @see Calendar#DST_OFFSET
   * @since 1.4
   */
  public int getOffset(long date) {
    if (inDaylightTime(new Date(date))) {
      return getRawOffset() + getDSTSavings();
    }
    return getRawOffset();
  }

  /**
   * Gets the raw GMT offset and the amount of daylight saving of this
   * time zone at the given time.
   *
   * @param date the milliseconds (since January 1, 1970, 00:00:00.000 GMT) at which the time zone
   * offset and daylight saving amount are found
   * @param offsets an array of int where the raw GMT offset (offset[0]) and daylight saving amount
   * (offset[1]) are stored, or null if those values are not needed. The method assumes that the
   * length of the given array is two or larger.
   * @return the total amount of the raw GMT offset and daylight saving at the specified date.
   * @see Calendar#ZONE_OFFSET
   * @see Calendar#DST_OFFSET
   */
  int getOffsets(long date, int[] offsets) {
    int rawoffset = getRawOffset();
    int dstoffset = 0;
    if (inDaylightTime(new Date(date))) {
      dstoffset = getDSTSavings();
    }
    if (offsets != null) {
      offsets[0] = rawoffset;
      offsets[1] = dstoffset;
    }
    return rawoffset + dstoffset;
  }

  /**
   * Sets the base time zone offset to GMT.
   * This is the offset to add to UTC to get local time.
   * <p>
   * If an underlying <code>TimeZone</code> implementation subclass
   * supports historical GMT offset changes, the specified GMT
   * offset is set as the latest GMT offset and the difference from
   * the known latest GMT offset value is used to adjust all
   * historical GMT offset values.
   *
   * @param offsetMillis the given base time zone offset to GMT.
   */
  abstract public void setRawOffset(int offsetMillis);

  /**
   * Returns the amount of time in milliseconds to add to UTC to get
   * standard time in this time zone. Because this value is not
   * affected by daylight saving time, it is called <I>raw
   * offset</I>.
   * <p>
   * If an underlying <code>TimeZone</code> implementation subclass
   * supports historical GMT offset changes, the method returns the
   * raw offset value of the current date. In Honolulu, for example,
   * its raw offset changed from GMT-10:30 to GMT-10:00 in 1947, and
   * this method always returns -36000000 milliseconds (i.e., -10
   * hours).
   *
   * @return the amount of raw offset time in milliseconds to add to UTC.
   * @see Calendar#ZONE_OFFSET
   */
  public abstract int getRawOffset();

  /**
   * Gets the ID of this time zone.
   *
   * @return the ID of this time zone.
   */
  public String getID() {
    return ID;
  }

  /**
   * Sets the time zone ID. This does not change any other data in
   * the time zone object.
   *
   * @param ID the new time zone ID.
   */
  public void setID(String ID) {
    if (ID == null) {
      throw new NullPointerException();
    }
    this.ID = ID;
  }

  /**
   * Returns a long standard time name of this {@code TimeZone} suitable for
   * presentation to the user in the default locale.
   *
   * <p>This method is equivalent to:
   * <blockquote><pre>
   * getDisplayName(false, {@link #LONG},
   *                Locale.getDefault({@link Locale.Category#DISPLAY}))
   * </pre></blockquote>
   *
   * @return the human-readable name of this time zone in the default locale.
   * @see #getDisplayName(boolean, int, Locale)
   * @see Locale#getDefault(Locale.Category)
   * @see Locale.Category
   * @since 1.2
   */
  public final String getDisplayName() {
    return getDisplayName(false, LONG,
        Locale.getDefault(Locale.Category.DISPLAY));
  }

  /**
   * Returns a long standard time name of this {@code TimeZone} suitable for
   * presentation to the user in the specified {@code locale}.
   *
   * <p>This method is equivalent to:
   * <blockquote><pre>
   * getDisplayName(false, {@link #LONG}, locale)
   * </pre></blockquote>
   *
   * @param locale the locale in which to supply the display name.
   * @return the human-readable name of this time zone in the given locale.
   * @throws NullPointerException if {@code locale} is {@code null}.
   * @see #getDisplayName(boolean, int, Locale)
   * @since 1.2
   */
  public final String getDisplayName(Locale locale) {
    return getDisplayName(false, LONG, locale);
  }

  /**
   * Returns a name in the specified {@code style} of this {@code TimeZone}
   * suitable for presentation to the user in the default locale. If the
   * specified {@code daylight} is {@code true}, a Daylight Saving Time name
   * is returned (even if this {@code TimeZone} doesn't observe Daylight Saving
   * Time). Otherwise, a Standard Time name is returned.
   *
   * <p>This method is equivalent to:
   * <blockquote><pre>
   * getDisplayName(daylight, style,
   *                Locale.getDefault({@link Locale.Category#DISPLAY}))
   * </pre></blockquote>
   *
   * @param daylight {@code true} specifying a Daylight Saving Time name, or {@code false}
   * specifying a Standard Time name
   * @param style either {@link #LONG} or {@link #SHORT}
   * @return the human-readable name of this time zone in the default locale.
   * @throws IllegalArgumentException if {@code style} is invalid.
   * @see #getDisplayName(boolean, int, Locale)
   * @see Locale#getDefault(Locale.Category)
   * @see Locale.Category
   * @see java.text.DateFormatSymbols#getZoneStrings()
   * @since 1.2
   */
  public final String getDisplayName(boolean daylight, int style) {
    return getDisplayName(daylight, style,
        Locale.getDefault(Locale.Category.DISPLAY));
  }

  /**
   * Returns a name in the specified {@code style} of this {@code TimeZone}
   * suitable for presentation to the user in the specified {@code
   * locale}. If the specified {@code daylight} is {@code true}, a Daylight
   * Saving Time name is returned (even if this {@code TimeZone} doesn't
   * observe Daylight Saving Time). Otherwise, a Standard Time name is
   * returned.
   *
   * <p>When looking up a time zone name, the {@linkplain
   * ResourceBundle.Control#getCandidateLocales(String, Locale) default
   * <code>Locale</code> search path of <code>ResourceBundle</code>} derived
   * from the specified {@code locale} is used. (No {@linkplain
   * ResourceBundle.Control#getFallbackLocale(String, Locale) fallback
   * <code>Locale</code>} search is performed.) If a time zone name in any
   * {@code Locale} of the search path, including {@link Locale#ROOT}, is
   * found, the name is returned. Otherwise, a string in the
   * <a href="#NormalizedCustomID">normalized custom ID format</a> is returned.
   *
   * @param daylight {@code true} specifying a Daylight Saving Time name, or {@code false}
   * specifying a Standard Time name
   * @param style either {@link #LONG} or {@link #SHORT}
   * @param locale the locale in which to supply the display name.
   * @return the human-readable name of this time zone in the given locale.
   * @throws IllegalArgumentException if {@code style} is invalid.
   * @throws NullPointerException if {@code locale} is {@code null}.
   * @see java.text.DateFormatSymbols#getZoneStrings()
   * @since 1.2
   */
  public String getDisplayName(boolean daylight, int style, Locale locale) {
    if (style != SHORT && style != LONG) {
      throw new IllegalArgumentException("Illegal style: " + style);
    }
    String id = getID();
    String name = TimeZoneNameUtility.retrieveDisplayName(id, daylight, style, locale);
    if (name != null) {
      return name;
    }

    if (id.startsWith("GMT") && id.length() > 3) {
      char sign = id.charAt(3);
      if (sign == '+' || sign == '-') {
        return id;
      }
    }
    int offset = getRawOffset();
    if (daylight) {
      offset += getDSTSavings();
    }
    return ZoneInfoFile.toCustomID(offset);
  }

  private static String[] getDisplayNames(String id, Locale locale) {
    return TimeZoneNameUtility.retrieveDisplayNames(id, locale);
  }

  /**
   * Returns the amount of time to be added to local standard time
   * to get local wall clock time.
   *
   * <p>The default implementation returns 3600000 milliseconds
   * (i.e., one hour) if a call to {@link #useDaylightTime()}
   * returns {@code true}. Otherwise, 0 (zero) is returned.
   *
   * <p>If an underlying {@code TimeZone} implementation subclass
   * supports historical and future Daylight Saving Time schedule
   * changes, this method returns the amount of saving time of the
   * last known Daylight Saving Time rule that can be a future
   * prediction.
   *
   * <p>If the amount of saving time at any given time stamp is
   * required, construct a {@link Calendar} with this {@code
   * TimeZone} and the time stamp, and call {@link Calendar#get(int)
   * Calendar.get}{@code (}{@link Calendar#DST_OFFSET}{@code )}.
   *
   * @return the amount of saving time in milliseconds
   * @see #inDaylightTime(Date)
   * @see #getOffset(long)
   * @see #getOffset(int, int, int, int, int, int)
   * @see Calendar#ZONE_OFFSET
   * @since 1.4
   */
  public int getDSTSavings() {
    if (useDaylightTime()) {
      return 3600000;
    }
    return 0;
  }

  /**
   * Queries if this {@code TimeZone} uses Daylight Saving Time.
   *
   * <p>If an underlying {@code TimeZone} implementation subclass
   * supports historical and future Daylight Saving Time schedule
   * changes, this method refers to the last known Daylight Saving Time
   * rule that can be a future prediction and may not be the same as
   * the current rule. Consider calling {@link #observesDaylightTime()}
   * if the current rule should also be taken into account.
   *
   * @return {@code true} if this {@code TimeZone} uses Daylight Saving Time, {@code false},
   * otherwise.
   * @see #inDaylightTime(Date)
   * @see Calendar#DST_OFFSET
   */
  public abstract boolean useDaylightTime();

  /**
   * Returns {@code true} if this {@code TimeZone} is currently in
   * Daylight Saving Time, or if a transition from Standard Time to
   * Daylight Saving Time occurs at any future time.
   *
   * <p>The default implementation returns {@code true} if
   * {@code useDaylightTime()} or {@code inDaylightTime(new Date())}
   * returns {@code true}.
   *
   * @return {@code true} if this {@code TimeZone} is currently in Daylight Saving Time, or if a
   * transition from Standard Time to Daylight Saving Time occurs at any future time; {@code false}
   * otherwise.
   * @see #useDaylightTime()
   * @see #inDaylightTime(Date)
   * @see Calendar#DST_OFFSET
   * @since 1.7
   */
  public boolean observesDaylightTime() {
    return useDaylightTime() || inDaylightTime(new Date());
  }

  /**
   * Queries if the given {@code date} is in Daylight Saving Time in
   * this time zone.
   *
   * @param date the given Date.
   * @return {@code true} if the given date is in Daylight Saving Time, {@code false}, otherwise.
   */
  abstract public boolean inDaylightTime(Date date);

  /**
   * Gets the <code>TimeZone</code> for the given ID.
   *
   * @param ID the ID for a <code>TimeZone</code>, either an abbreviation such as "PST", a full name
   * such as "America/Los_Angeles", or a custom ID such as "GMT-8:00". Note that the support of
   * abbreviations is for JDK 1.1.x compatibility only and full names should be used.
   * @return the specified <code>TimeZone</code>, or the GMT zone if the given ID cannot be
   * understood.
   */
  public static synchronized TimeZone getTimeZone(String ID) {
    return getTimeZone(ID, true);
  }

  /**
   * Gets the {@code TimeZone} for the given {@code zoneId}.
   *
   * @param zoneId a {@link ZoneId} from which the time zone ID is obtained
   * @return the specified {@code TimeZone}, or the GMT zone if the given ID cannot be understood.
   * @throws NullPointerException if {@code zoneId} is {@code null}
   * @since 1.8
   */
  public static TimeZone getTimeZone(ZoneId zoneId) {
    String tzid = zoneId.getId(); // throws an NPE if null
    char c = tzid.charAt(0);
    if (c == '+' || c == '-') {
      tzid = "GMT" + tzid;
    } else if (c == 'Z' && tzid.length() == 1) {
      tzid = "UTC";
    }
    return getTimeZone(tzid, true);
  }

  /**
   * Converts this {@code TimeZone} object to a {@code ZoneId}.
   *
   * @return a {@code ZoneId} representing the same time zone as this {@code TimeZone}
   * @since 1.8
   */
  public ZoneId toZoneId() {
    String id = getID();
    if (ZoneInfoFile.useOldMapping() && id.length() == 3) {
      if ("EST".equals(id)) {
        return ZoneId.of("America/New_York");
      }
      if ("MST".equals(id)) {
        return ZoneId.of("America/Denver");
      }
      if ("HST".equals(id)) {
        return ZoneId.of("America/Honolulu");
      }
    }
    return ZoneId.of(id, ZoneId.SHORT_IDS);
  }

  private static TimeZone getTimeZone(String ID, boolean fallback) {
    TimeZone tz = ZoneInfo.getTimeZone(ID);
    if (tz == null) {
      tz = parseCustomTimeZone(ID);
      if (tz == null && fallback) {
        tz = new ZoneInfo(GMT_ID, 0);
      }
    }
    return tz;
  }

  /**
   * Gets the available IDs according to the given time zone offset in milliseconds.
   *
   * @param rawOffset the given time zone GMT offset in milliseconds.
   * @return an array of IDs, where the time zone for that ID has the specified GMT offset. For
   * example, "America/Phoenix" and "America/Denver" both have GMT-07:00, but differ in daylight
   * saving behavior.
   * @see #getRawOffset()
   */
  public static synchronized String[] getAvailableIDs(int rawOffset) {
    return ZoneInfo.getAvailableIDs(rawOffset);
  }

  /**
   * Gets all the available IDs supported.
   *
   * @return an array of IDs.
   */
  public static synchronized String[] getAvailableIDs() {
    return ZoneInfo.getAvailableIDs();
  }

  /**
   * Gets the platform defined TimeZone ID.
   **/
  private static native String getSystemTimeZoneID(String javaHome);

  /**
   * Gets the custom time zone ID based on the GMT offset of the
   * platform. (e.g., "GMT+08:00")
   */
  private static native String getSystemGMTOffsetID();

  /**
   * Gets the default {@code TimeZone} of the Java virtual machine. If the
   * cached default {@code TimeZone} is available, its clone is returned.
   * Otherwise, the method takes the following steps to determine the default
   * time zone.
   *
   * <ul>
   * <li>Use the {@code user.timezone} property value as the default
   * time zone ID if it's available.</li>
   * <li>Detect the platform time zone ID. The source of the
   * platform time zone and ID mapping may vary with implementation.</li>
   * <li>Use {@code GMT} as the last resort if the given or detected
   * time zone ID is unknown.</li>
   * </ul>
   *
   * <p>The default {@code TimeZone} created from the ID is cached,
   * and its clone is returned. The {@code user.timezone} property
   * value is set to the ID upon return.
   *
   * @return the default {@code TimeZone}
   * @see #setDefault(TimeZone)
   */
  public static TimeZone getDefault() {
    return (TimeZone) getDefaultRef().clone();
  }

  /**
   * Returns the reference to the default TimeZone object. This
   * method doesn't create a clone.
   */
  static TimeZone getDefaultRef() {
    TimeZone defaultZone = defaultTimeZone;
    if (defaultZone == null) {
      // Need to initialize the default time zone.
      defaultZone = setDefaultZone();
      assert defaultZone != null;
    }
    // Don't clone here.
    return defaultZone;
  }

  private static synchronized TimeZone setDefaultZone() {
    TimeZone tz;
    // get the time zone ID from the system properties
    String zoneID = AccessController.doPrivileged(
        new GetPropertyAction("user.timezone"));

    // if the time zone ID is not set (yet), perform the
    // platform to Java time zone ID mapping.
    if (zoneID == null || zoneID.isEmpty()) {
      String javaHome = AccessController.doPrivileged(
          new GetPropertyAction("java.home"));
      try {
        zoneID = getSystemTimeZoneID(javaHome);
        if (zoneID == null) {
          zoneID = GMT_ID;
        }
      } catch (NullPointerException e) {
        zoneID = GMT_ID;
      }
    }

    // Get the time zone for zoneID. But not fall back to
    // "GMT" here.
    tz = getTimeZone(zoneID, false);

    if (tz == null) {
      // If the given zone ID is unknown in Java, try to
      // get the GMT-offset-based time zone ID,
      // a.k.a. custom time zone ID (e.g., "GMT-08:00").
      String gmtOffsetID = getSystemGMTOffsetID();
      if (gmtOffsetID != null) {
        zoneID = gmtOffsetID;
      }
      tz = getTimeZone(zoneID, true);
    }
    assert tz != null;

    final String id = zoneID;
    AccessController.doPrivileged(new PrivilegedAction<Void>() {
      @Override
      public Void run() {
        System.setProperty("user.timezone", id);
        return null;
      }
    });

    defaultTimeZone = tz;
    return tz;
  }

  /**
   * Sets the {@code TimeZone} that is returned by the {@code getDefault}
   * method. {@code zone} is cached. If {@code zone} is null, the cached
   * default {@code TimeZone} is cleared. This method doesn't change the value
   * of the {@code user.timezone} property.
   *
   * @param zone the new default {@code TimeZone}, or null
   * @throws SecurityException if the security manager's {@code checkPermission} denies {@code
   * PropertyPermission("user.timezone", "write")}
   * @see #getDefault
   * @see PropertyPermission
   */
  public static void setDefault(TimeZone zone) {
    SecurityManager sm = System.getSecurityManager();
    if (sm != null) {
      sm.checkPermission(new PropertyPermission
          ("user.timezone", "write"));
    }
    defaultTimeZone = zone;
  }

  /**
   * Returns true if this zone has the same rule and offset as another zone.
   * That is, if this zone differs only in ID, if at all.  Returns false
   * if the other zone is null.
   *
   * @param other the <code>TimeZone</code> object to be compared with
   * @return true if the other zone is not null and is the same as this one, with the possible
   * exception of the ID
   * @since 1.2
   */
  public boolean hasSameRules(TimeZone other) {
    return other != null && getRawOffset() == other.getRawOffset() &&
        useDaylightTime() == other.useDaylightTime();
  }

  /**
   * Creates a copy of this <code>TimeZone</code>.
   *
   * @return a clone of this <code>TimeZone</code>
   */
  public Object clone() {
    try {
      TimeZone other = (TimeZone) super.clone();
      other.ID = ID;
      return other;
    } catch (CloneNotSupportedException e) {
      throw new InternalError(e);
    }
  }

  /**
   * The null constant as a TimeZone.
   */
  static final TimeZone NO_TIMEZONE = null;

  // =======================privates===============================

  /**
   * The string identifier of this <code>TimeZone</code>.  This is a
   * programmatic identifier used internally to look up <code>TimeZone</code>
   * objects from the system table and also to map them to their localized
   * display names.  <code>ID</code> values are unique in the system
   * table but may not be for dynamically created zones.
   *
   * @serial
   */
  private String ID;
  private static volatile TimeZone defaultTimeZone;

  static final String GMT_ID = "GMT";
  private static final int GMT_ID_LENGTH = 3;

  // a static TimeZone we can reference if no AppContext is in place
  private static volatile TimeZone mainAppContextDefault;

  /**
   * Parses a custom time zone identifier and returns a corresponding zone.
   * This method doesn't support the RFC 822 time zone format. (e.g., +hhmm)
   *
   * @param id a string of the <a href="#CustomID">custom ID form</a>.
   * @return a newly created TimeZone with the given offset and no daylight saving time, or null if
   * the id cannot be parsed.
   */
  private static final TimeZone parseCustomTimeZone(String id) {
    int length;

    // Error if the length of id isn't long enough or id doesn't
    // start with "GMT".
    if ((length = id.length()) < (GMT_ID_LENGTH + 2) ||
        id.indexOf(GMT_ID) != 0) {
      return null;
    }

    ZoneInfo zi;

    // First, we try to find it in the cache with the given
    // id. Even the id is not normalized, the returned ZoneInfo
    // should have its normalized id.
    zi = ZoneInfoFile.getZoneInfo(id);
    if (zi != null) {
      return zi;
    }

    int index = GMT_ID_LENGTH;
    boolean negative = false;
    char c = id.charAt(index++);
    if (c == '-') {
      negative = true;
    } else if (c != '+') {
      return null;
    }

    int hours = 0;
    int num = 0;
    int countDelim = 0;
    int len = 0;
    while (index < length) {
      c = id.charAt(index++);
      if (c == ':') {
        if (countDelim > 0) {
          return null;
        }
        if (len > 2) {
          return null;
        }
        hours = num;
        countDelim++;
        num = 0;
        len = 0;
        continue;
      }
      if (c < '0' || c > '9') {
        return null;
      }
      num = num * 10 + (c - '0');
      len++;
    }
    if (index != length) {
      return null;
    }
    if (countDelim == 0) {
      if (len <= 2) {
        hours = num;
        num = 0;
      } else {
        hours = num / 100;
        num %= 100;
      }
    } else {
      if (len != 2) {
        return null;
      }
    }
    if (hours > 23 || num > 59) {
      return null;
    }
    int gmtOffset = (hours * 60 + num) * 60 * 1000;

    if (gmtOffset == 0) {
      zi = ZoneInfoFile.getZoneInfo(GMT_ID);
      if (negative) {
        zi.setID("GMT-00:00");
      } else {
        zi.setID("GMT+00:00");
      }
    } else {
      zi = ZoneInfoFile.getCustomTimeZone(id, negative ? -gmtOffset : gmtOffset);
    }
    return zi;
  }
}
